Have said individual email the LISTSERV@listhost the command

THANKS

If she gets an appropriate response, then it is either a list problem
(maybe she is being filtered?), a LISTSERV Distribute backbone-related
problem (a LISTSERV host might be in somebody's anti-relay rules), an MX
hosting problem, a DNS problem, or something related to anti-spam.

These are all speculations of course since you provided zero information
other than naming a country.

/Pete